There is a strong need to increase the capacity and flexibility of photonic transport networks. The evolving telecommunication networks are increasingly focusing on flexibility and reconfigurability, which requires enhanced functionality of photonic integrated circuits (PICs) for optical communications, as well as compact devices. The interest for multi-mode interference (MMI) effects in integrated optics for single-mode transmission systems has recently been increasing. Optical devices based on MMI effects have large optical bandwidth, are polarization insensitive and sustain high fabrication tolerances to mention a few advantages. The operation of MMI waveguide devices is based on the self-imaging principle and is further described in “Optical Multi-Mode Interference Devices Based on Self-Imaging: Principles and Applications” by L. B Soldano and E. C. M. Pennings published in J. of Lightwave Technology, Vol. 13, No. 4 April 1995.
MMI waveguide devices have applications in a number of different areas, for instance, as a wavelength selective switch, as described in “Bragg-grating assisted MMIMI coupler for wavelength selective switching” by the present inventor published in Electronics Letters 10th December 1998, Vol. 34, No. 25. In this paper the present inventor describes a novel optical device for wavelength selective switching. The device is based on a Bragg grating assisted MMIMI (Multi Mode Interference Michelson Interferometer) coupler.
Another application for a MMI waveguide device is as a coupler, as described in the paper “Multimode Interference Couplers with Tuneable Splitting Ratios” by J. Leuthold and C. H. Joyner, published in Proc. ECOC September 2000, Münich Vol. 3. In this paper the authors present a novel, compact multi-mode interference coupler with tuneable power splitting ratios. The coupler has large tuning ranges and is used to optimise on-off ratios in interferometric devices or is even used as a switch.
Multiplexing of optical signals is described in “Transmission Characteristics of Arrayed Waveguide N×N wavelength Multiplexer”, in J. of Lightwave Technology Vol 13(3), pp 447-445, 1995 by H. takahasi, K. Oda, H. Toba and Y. Inoue.
The need to be able to multiplex or demultiplex optical signals in optical telecommunication networks is apparent. Simple space switching of broadband signals allows routing based on for instance available capacity or rerouting around parts of the network currently unavailable, and wavelength switching is an important feature of any flexible optical network.